Tuesday, April 22, 2014

IPCC Working Group III released its AR5 report on mitigation last week, and one effect was to give a considerable boost to the visibility and credibility of CDR, in particular BECCS. It has been less than five years since the Royal Society report was released, and until recently CDR and BECCS were generally unknown acronyms. Yet now CDR methods have been incorporated into IPCC mitigation scenarios so deeply that, in the view of WGIII, achieving the 2C target (let alone 1.5C) is very difficult without reliance on negative emissions technologies (similar assumptions are now built into UK government scenarios.) It is worth quoting the Summary for Policymakers discussion of CDR at some length:

Mitigation scenarios reaching about 450 ppm CO2eq in 2100 [i.e., 2C] typically involve temporary overshoot of atmospheric concentrations, as do many scenarios reaching about 500 ppm to 550 ppm CO2eq in 2100. Depending on the level of the overshoot, overshoot scenarios typically rely on the availability and widespread deployment of BECCS and afforestation in the second half of the century. The availability and scale of these and other Carbon Dioxide Removal (CDR) technologies and methods are, to varying degrees, associated with challenges and risks … CDR is also prevalent in many scenarios without overshoot to compensate for residual emissions from sectors where mitigation is more expensive (p. 15).

As the summary notes, there are real risks associated with BECCS and other NETs, such as potential land-use and food security issues related to biomass cultivation. But there are serious risks associated with surpassing 450 ppm, arguably bigger risks than those connected to most CDR techniques. In the end, climate policy involves risk trade-offs, whether those trade-offs apply to mitigation, adaptation, geoengineering, or all three. The IPCC has done policy-makers a great service by emphasizing the significant risks entailed in not taking BECCS and other forms of CDR seriously.